Mechanistic Aspects of Os(VIII)/Ru(III) Catalysed Oxidation of L-phenylalanine by Ag(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of L-phenylalanine (L-Pal) by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at 27 °C and a constant ionic strength of 0.25 mol dm^?3 was studied spectrophotometrically. The involvement of free radicals was observed in the reactions. The reaction between DPA and L-Pal in alkaline medium exhibits stoichiometry as [L-Pal]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)], [Ru(III)] and [DPA] and has negative fractional order in [IO₄ ^?]. It has less than unit order in [L-Pal] and [OH^?]. However, the order in [L-Pal] and [OH^?] changes from first order to zero order as their concentrations increase. The main oxidation products were identified by spot test and spectral studies. The probable mechanisms were proposed and discussed. The catalytic constant (K _c) was also calculated for Os(VIII) and Ru(III) catalysis at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified.     

Ru(III)/Os(VIII) Catalysed Oxidation of Gabapentin (Neurotin) Drug by Diperiodatoargentate(III) in Aqueous Alkaline Medium (Stopped Flow Technique): A Comparative Study

The kinetics of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalysed oxidation of neuroleptic drug, gabapentin (GBP) by diperiodatoargentate(III) (DPA) in alkaline medium at 27 °C and a constant ionic strength of 0.60 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases are 1-(hydroxymethyl) cyclohexane acetic acid and Ag(I). The stoichiometry is the same in both the catalysed reactions i.e. [gabapentin]:[DPA] = 1:1. The reaction is of first order in Os(VIII)/Ru(III) and [DPA] and has less than unit order in both [GBP] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)/Ru(III)-gabapentin complex, which further reacts with one mole of monoperiodatoargentate(III) (MPA) species in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectroscopic studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant (K _c) was also calculated for both catalysed reactions at different temperatures. From the plots of log K _c versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII)>Ru(III). The probable active species of catalyst and oxidant have been identified.     

Osmium(VIII)/Ruthenium(III) Catalysed Oxidation of l-lysine by Diperiodatocuprate(III) in Aqueous Alkaline Medium: A Comparative Mechanistic Approach by Stopped Flow Technique

Abstract The kinetics of osmium(VIII) and ruthenium(III) catalysed oxidation of l-lysine (l-lys) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.15 mol dm⁻³ was studied spectrophotometrically. The reaction between l-lys and DPC in alkaline medium exhibits 1:2 stoichiometry in both catalysed reaction (l-lys: DPC). The reaction is first order in [DPC] and has less than unit order both in [l-lys] and [alkali]. Increase in periodate concentration decreases the rate. Intervention of free radicals was observed in the reaction. The main products were identified by spot test, IR and GC-MS studies. Probable mechanisms are proposed and discussed. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII) > Ru(III). The active species of catalyst and oxidant have been identified. Graphical Abstract The kinetic and mechanistic investigations of the reaction between DPC and l-lysine has been studied in presence of microamounts of ruthenium(III) and osmium(VIII) in alkaline medium. The monoperiodatoargentate(III), [Ru(H₂O)₅OH]²⁺ and [OsO₄(OH)₂]²⁻ are considered as the active species of oxidant, DPC, ruthenium(III) and osmium(VIII) respectively.      

Oxidative decolorisation of Eriochrome Black T with Chloramine‐T: kinetic,mechanistic, and spectrophotometric approaches

The kinetics and mechanism of oxidative decolorisation of Eriochrome Black T (EBT) with sodium N‐chloro‐p‐toluenesulfonamide or Chloramine‐T (CAT), catalysed by osmium tetroxide [Os(VIII)] in alkaline medium and uncatalysed in acid medium, have been spectrophotometrically investigated at 303 K. The reaction exhibited a first‐order dependence of rate on [CAT]₀ and [EBT]₀ in both media, and also with respect to [H⁺]. The order with respect to [OH^‐] and [Os(VIII)] was fractional. Activation parameters were deduced. It was observed that the uncatalysed decolorisation reaction was ca. eightfold faster in acid medium in comparison with alkaline medium, while the Os(VIII)‐catalysed reaction was ca. sevenfold faster than the uncatalysed reaction. Mechanisms and rate laws were determined. The chemical oxygen demand of Eriochrome Black T dye was also determined. Importantly, the developed oxidative decolorisation method is simple, efficient, inexpensive, requires less time, and is environmentally benign. Hence, it can be adapted for treating Eriochrome Black T present in industrial and laboratory wastewater.     

Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid—a kinetics and mechanistic approach

The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm^?3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH^? species to form a hydroxide species and reacts with [Fe(CN)₆]^3? in slow step to form an intermediate species(C₁). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)₆]^3?. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.     

<Emphasis Type="Italic">Meso</Emphasis>-Tetra-(3,5-Dibromo-4-Hydroxydroxyphenyl) Porphyrin Copper (II) Self-Assembled Modified Gold Electrode Through <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine: The Preparation,Electrochemical Behavior and its Application

In this study, a sensor for the sensitive determination of ascorbic acid (AA) has been fabricated based on meso-tetra-(3,5-dibromo-4-hydroxydroxyphenyl) porphyrin copper (II) (T(DBHP)P-Cu) modified Au electrode through l-cysteine (l-cys). Firstly, l-cys modified Au electrode was prepared through self-assembled technology. Then T(DBHP)P-Cu was adsorbed on l-cys/Au through covalent binding. The fabrication process and electrochemical behavior of T(DBHP)P-Cu/l-cys/Au were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that AA exhibited good electrochemical activity at T(DBHP)P-Cu/l-cys/Au. The oxidation peak current increased linearly with AA concentration in the range of 1.00 × 10⁻³–1.02 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.41 × 10⁻⁷ mol L⁻¹. Additionally, the modified electrode could be applied to the detect AA in practical samples.     

Electrochemical assembly of [Ru(bpy)<Subscript>2</Subscript>tatp]<Superscript>2+</Superscript> associated with surfactants on the MWNTs/GC electrode

The electrochemical assembly of [Ru(bpy)₂tatp]²⁺ (where bpy = 2,2′-bipyridine, tatp = 1,4,8,9-tetra-aza-triphenylene) on the multi-walled carbon nanotubes-modified glassy carbon electrode (MWNTs/GC) in the presence of anionic and cationic surfactants has been investigated. A diffusion-controlled wave and three prewaves are exhibited on the differential pulse voltammogram of [Ru(bpy)₂tatp]²⁺. The formal potential of the prewaves is found to be much negative than that of the diffusion-controlled wave. An appropriate amount of anionic surfactants including dihexadecyl phosphate (DHP) and deoxyribonucleic acid (DNA) can prompt the assembly of [Ru(bpy)₂tatp]²⁺ on the MWNTs/GC electrode by using the method of repetitive voltammetric sweeping. In contrast, cationic surfactant such as hexadecyl trismethyl ammonium chrolide (HTAC) dispersed on the MWNTs surface is found to inhibit the assembly of [Ru(bpy)₂tatp]²⁺. Meanwhile, the assembled principle of [Ru(bpy)₂tatp]²⁺ on the MWNTs/GC electrode with the participation of surfactants is discussed in detail.     

Kinetics and Mechanism of Ru(III)-Catalyzed Oxidation of Paracetamol by Chloramine-T in Aqueous Acidic Medium

The present paper deals with the kinetics and mechanism of Ru(III)-catalyzed oxidation of paracetamol by chloramine-T (CAT) in aqueous perchloric acid medium at 303 K. The experimental result shows a first order dependence on paracetamol at its low concentrations, but tending towards zeroth order at its higher concentrations. The reactions follow a first order rate dependence with respect to oxidant [CAT] and [Ru(III)]. The reaction showed negative fractional-order dependence on the rate for [H⁺] and p-toluenesulphonamide. Variation in [Cl^?] and ionic strength of the medium did not bring about any significant change on the rate of reaction. The decrease in the reaction rate with decrease in the dielectric constant of the medium was observed in the oxidation of paracetamol. Kinetic and equivalence studies together with product analysis, observed effect of dielectric constant of the medium on the rate of reaction and activation parameters furnished a basis for the formation of a common reaction mechanism for the Ru(III)-catalyzed oxidation of paracetamol by CAT in the acidic medium.     

Synthesis and characterization of new optically active poly(amide-imide)s containing 1,3,4-oxadiazole moiety in the main chain

Six new optically active poly(amide-imide)s were synthesized by poly condensation reaction of 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (8) with six chiral N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)-bis-l-amino acids (3a–f) in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenylphosphite (TPP), calcium chloride (CaCl₂), and pyridine. Chiral N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)-bis-l-amino acids (3a–f) were obtained by the reaction of bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (1) with two equimolar of l-alanine (2a), l-valine (2b), l-leucine (2c), l-isoleucine (2d), l-phenyl alanine (2e), and l-2-aminobutyric acid (2f) in acetic acid. The poly condensation reaction produced a series of novel poly(amide-imide)s (9a–f) in high yield and with inherent viscosities between 0.30 and 0.52 dL/g. The resulting polymers were characterized by elemental analysis, viscosity measurement, solubility testing, thermo-gravimetric analysis (TGA), ¹H-NMR, and FT-IR techniques.     

Multi-walled carbon nanotubes (MWCNTs) and room temperature ionic liquids (RTILs) carbon paste Er(III) sensor based on a new derivative of dansyl chloride

Solution studies showed the strong interaction of [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (NSP) with Er(III) ions. NSP was used as a sensing material during construction of carbon paste Er(III) sensors. The electrodes were modified with 1-n-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF₄, as room temperature ionic liquid (RTIL) and multi-walled carbon nanotube (MWCNT). Potentiometric sensors constructed with [bmim]BF₄ and MWCNTs show better sensitivity, selectivity, response time, and response stability compared to Er(III) carbon paste sensors. The best performance for the modified sensor was obtained with an electrode composition of 20% [bmim]BF₄, 20% NSP, 45% graphite powder and 15% MWCNT. This particular sensor formulation exhibits a Nernstian response (19.8 ± 0.3 mV decade⁻¹) toward Er(III) ions in the range of 1.0 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁸ mol L⁻¹. The proposed modified Er(III) sensor can be used over the pH range from 3.5 to 9.0.     

Effects of antimony(III) on zinc electrodeposition from acidic sulfate electrolyte containing [BMIM]HSO<Subscript>4</Subscript>

The effect of antimony(III) on the cathodic current efficiency (CE), power consumption (PC), deposit morphology, and polarization behavior during electrodeposition of zinc from acidic sulfate solutions containing 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ was investigated. The results indicated that the addition of Sb(III) alone decreased the CE, increased the PC, and deteriorated the quality of the zinc electrodeposits. However, the combined addition of Sb(III) and [BMIM]HSO₄ was found to be beneficial for zinc deposition and improved the surface morphology of the zinc electrodeposits. Maximum CE and minimum PC were obtained at the combined addition of 0.02 mg dm⁻³ Sb(III) and 5 mg dm⁻³ [BMIM]HSO₄. Depolarization of the cathode was noted in the presence of Sb(III) alone in the electrolyte whereas this effect was partly counteracted by the addition of [BMIM]HSO₄. Cathodic polarization curves were traced and analyzed to determine the electrokinetic parameters such as Tafel slope, transfer coefficient, and exchange current density so as to elucidate the nature of the electrode reactions. The data obtained from X-ray diffractogram revealed that the presence of Sb(III) did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

Intraligand fluorescence of M(III)(oxinate)3 under ambient conditions with M = Fe,Ru, Os and oxinate = 8-quinolinolate

The electronic spectra of the complexes M(III)(oxinate)₃ with M = Fe, Ru, Os and oxinate = 8-quinolinolate are dominated by oxinate to M(III) LMCT transitions. Nevertheless, these complexes are also characterized by a fluorescence at higher energies, which originates from the oxinate ligands. This green luminescence appears in solution as well as in the solid state under ambient conditions. The electronic coupling between the IL and the LMCT states is apparently not strong enough to lead to a complete quenching of the oxinate IL fluorescence.     

Synthesis and characterization of trans-[Ru(NO)Cl(L)4](PF6)2 (L = isonicotinamide; 4-acetylpyridine) and related species

The trans-[RuCl₂(L)₄], trans-[Ru(NO)Cl (L)₄](PF₆)₂ (L = isonicotinamide and 4-acetylpyridine) and trans-[Ru(NO)(OH)(py)₄]Cl₂ (py = pyridine) complexes have been prepared and characterized by elemental analysis, UV–visible, infrared, and ¹H NMR spectroscopies, and cyclic voltammetry. The MLCT band energies of trans-[RuCl₂(L)₄] increase in the order 4-acpy < isn < py. The reduction potentials of trans-[RuCl₂(L)₄] and trans-[Ru(NO)Cl(L)₄]²⁺ increase in the order py < isn < 4-acpy. The stretching band frequency, ν_NO, of the nitrosyl complexes ranges from 1913 to 1852 cm^?1 indicating a nitrosonium character for the NO ligand. Due to the large π-acceptor ability of the equatorial ligands, the coordinated water is much more acidic in the water soluble trans-[Ru(NO)(H₂O)(py)₄]³⁺ than in trans-[Ru(NO)(H₂O)(NH₃)₄]³⁺.     

Extraction behavior of Am(III) and Eu(III) by tri-n-octylmethylammonium diglycolamate ionic liquid impregnated XAD-7

Aliquat-336-based strongly hydrophobic ionic liquid, tri-n-octylmethylammonium diglycolamate ([A336]⁺[DGA]^?), was prepared and impregnated in Amberlite XAD-7 (abbreviated as [A336]⁺[DGA]^?/XAD-7) for studying the extraction behavior of Am(III) and Eu(III) from nitric acid medium. The distribution ratio of Am(III) and Eu(III) in [A336]⁺[DGA]^?/XAD-7 decreased with an increase in the concentration of nitric acid and the mechanism of trivalent metal ion extraction in the resin phase was elucidated. The uptake of Am(III) and Eu(III) in [A336]⁺[DGA]^?/XAD-7 followed a second order and from the Langmuir adsorption model the apparent europium extraction capacity was determined. The conditions needed for efficient separation of Am(III) from Eu(III) was optimized.     

Synthesis and characterization of star-shaped poly(d,l-lactide)-block-poly(ethylene glycol) copolymers

Star-shaped hydroxy-terminated poly(d,l-lactide) (s-PDLLA), with arms of different lengths, were obtained by ring-opening polymerization (ROP) of d,l-lactide (LA) initiated by varied contents of pentaerythritol (PETH) in the presence of stannous octoate (Sn(Oct)₂), and were condensed with carboxyl-terminated poly(ethylene glycol) methyl ether (CT-mPEG, M _n = 850 and 2,000) to afford four-arm star-shaped poly(d,l-lactide)-block-poly(ethylene glycol) copolymer (s-PDLLA-b-PEG). The polymers, including s-PDLLA, CT-mPEG, and s-PDLLA-b-PEG, were characterized and confirmed by ¹H-NMR and ¹³C-NMR spectroscopy, fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC).     

Synthesis of poly(lactic acid)-poly(phenyl phosphate) via direct polycondensation and its characterization

Starting from d,l-lactic acid (d,l-LA), ethylene glycol (EG) and phenyl dichlorophosphate (PDP), poly(lactic acid)-poly(phenyl phosphate) was synthesized via direct copolycondensation. The novel poly(lactic acid) (PLA) copolymer containing phosphorus was characterized with FTIR, ¹H NMR, ³¹P NMR, GPC, and DSC. The GPC results showed that, after the prepolymerization of d,l-LA and EG, the direct melt copolymerization of oligomer and PDP gave copolymer with higher weight-average molecular (Mw) than the direct solution copolymerization. The optimal synthetic conditions of the direct melt copolymerization, including prepolymerization method, catalyst kinds and quantity, copolymerization temperature and time, were all discussed in detail. When catalyzed by 0.5% (weight percent) ZnO under 160°C and 70 Pa, 8 h’s copolymerization gave the copolymer with maximum Mw 9,200 Da. When the feed molar ratio of d,l-LA/EG/PDP was 20/1/1 instead of 20/1/2, the melt polymerization under the above conditions gave the copolymer with maximum Mw 27,700 Da (Mw/Mn 1.07). The novel one-step method could be an alternative route to the synthesis of poly(lactic acid)-poly(phosphate ester) instead of the traditional two-step method using lactide as intermediate. At the same time, the novel PLA copolymer containing phosphorus with phenyl group may give this material more chance for the further structure modification as expected.     

Highly selective solvent extraction of Zn(II) and Cr(III) with trioctylmethylammonium chloride ionic liquid

This study investigates the recovery of Zn(II) and Cr(III) from aqueous solutions based on solvent extraction with trioctylmethylammonium chloride [TOMA⁺][Cl-], commercialy named Aliquat 336. Single metal solutions and binary mixtures of both metals were considered. The effect of relevant operating conditions such as pH, contact time, initial concentration, O/A phase volumetric ratio, and temperature were evaluated. Additionally, loading capacity and stripping studies were performed. Results showed that [TOMA⁺][Cl^?] is an effective extracting agent for Zn(II), reaching maximum removal capacity at pH 1.8 and demonstrating fast extraction kinetics. Extraction efficiencies above 99% were achieved at 0.5, 0.75, and 1.00 O/A volumetric phase ratios for 0.1 g/L initial Zn(II) concentration. At 1 g/L and 10 g/L concentration, for the same O/A ratios, approximately 88% of the initial Zn(II) was extracted. In contrast, it was found that negligible amounts of Cr(III) were transferred to the [TOMA⁺][Cl^?] phase at the 1-5 pH range. Selectivity studies showed that Zn(II) removal is boosted in the presence of Cr(III), although no Cr(III) is extracted. [TOMA⁺][Cl^?] exhibited a high Zn(II) storage capacity, since after 25 loading cycles with 1 g/L, the loading capacity reached approximately 13.5 g/L, and after five loading cycles with 5 g/L, the capacity reached 19.4 g/L. Stripping tests revealed that NaOH is an efficient agent for the removal of Zn(II) from the ionic liquids, reaching 98.5% removal after two cycles, whereas HNO₃ is not a suitable agent, reaching less than 40% removal after three cycles. [TOMA⁺][Cl^?] revealed high potential for separating Zn(II) from Cr(III).     

Sensibilisierte Photolyse von Bis(dimethylglyoximato)cobalt(III)-Komplexen mit axial koordiniertem Azid bzw. Thiophenolat als photochemischen Opferliganden

Sensitized Photolysis of Bis(dimethylglyoximato)cobalt(III) Complexes with Axially Coordinated Azide or Thiophenolate as Photochemical Sacrificial Ligands The photolysis of [N₃Co(dmg)₂pyr] 1a and [PhSCo(dmg)₂pyr] 1b (dmg = dimethylglyoxime, pyr = pyridine) is sensitized by both [Ru(bpy)₃]Cl₂ 2 (bpy = 2,2′-bipyridine) and Michler's thioketone 3 (4,4′-bis(dimethyl-amino)-thiobenzophenone). Quenching of 2 by the cobalt(III) chelates 1a and 1b was studied by luminescence spectroscopy. The quenching rate constants calculated are in the order of magnitude of k_q ≅ 10⁶ mol⁻¹ s⁻¹. Polychromatic irradiation (> 250 nm) of 1b and 3 in the presence of thiophenole (PhSH) leads to hydrogen evolution, whereas long-wavelength (546 nm) irradiation does not. The results of these sensitization experiments support strongly a mechanism of catalyzed photolysis of PhSH as proposed earlier.     

Photoinitiation of methyl methacrylate with a novel iron (III) oxalato complex

Summary The photopolymerization of methyl methacrylate (MMA) by the photoinitiator iron (III) tris (oxalato) ferrate(III) tetrahydrate, Fe[Fe(C₂O₄)₃] . 4H₂O (A) has been studied under UV radiation of 254 nm at 35°C in DMSO. The initial rate of polymerization, R_p is proportional to [MMA]^1.11±0.13. R_p also varies linearly with the square root of [A] up to 5.00 X 10^-4 mol l^-1 and above this concentration, R_p decreases with the increase of [A]. It is likely that at a higher concentration of the complex A, the termination of the polymer chain occurs through interaction between the molecules of the complex. A suitable mechanism has been proposed to explain the kinetics of the reaction.     

A Novel Oxidation of Valine by N-Bromophthalimide in the Presence of Ruthenium(III) Chloride as a Homogeneous Catalyst

Kinetics of Ruthenium(III) [Ru(III)] chloride catalyzed oxidation of valine (Val) has been studied by N-bromophthalimide (NBP) in the acidic medium at 35 °C. The reaction rate follows first-order and zero-order dependence with respect to [NBP] and [Val]. First-order kinetics was observed for Ru(III) chloride at low range of concentrations and tending towards zero-order at higher concentrations. A negative effect was observed for [H⁺] and [phthalimide], while a positive effect was observed for [Cl^?] on the reaction rate. Hg(OAc)₂, ionic strength (I), and dielectric constant (D) of the medium did not change significantly the reaction rate. The rate constants as a function of temperature (298–318 K) were used to calculate activation parameters of the oxidation of Val by NBP. A plausible mechanism was proposed to explain the results of kinetic studies, reaction stoichiometry and product analysis.